MIDI (Musical Instrument Digital Interface) is a standard known in the art that enables digital musical instruments and processors of digital music, such as personal computers and sequencers, to communicate data about musical tones. Information regarding implementing the MIDI standard is widely available, and can be found, for instance, in a publication entitled "Official MIDI Specification" (MIDI Manufacturers Association, La Habra, Calif.), which is incorporated herein by reference.
Data used in the MIDI standard typically include times of depression and release of a specified key on a digital musical instrument, the velocity of the depression, optional post-depression pressure measurements, vibrato, tremolo, etc. Analogous to a text document in a word processor, a performance by one or more digital instruments using the MIDI protocol can be processed at any later time using standard editing tools, such as insert, delete, and cut-and-paste, until all aspects of the performance are in accordance with the desires of a user of the musical editor.
Notably, a MIDI computer file, which contains the above-mentioned data representing a musical performance, does not contain a representation of the actual wave forms generated by an output module of the original performing musical instrument. Rather, the file may contain an indication that, for example, certain musical notes should be played by a simulated acoustic grand piano. A MIDI-compatible output device subsequently playing the file would then retrieve from its own memory a representation of an acoustic grand piano, which representation may be the same as or different from that of the original digital instrument. The retrieved representation is used to generate the musical wave forms, based on the data in the file.
MIDI files and MIDI devices which process MIDI information designate a desired simulated musical instrument to play forthcoming notes by indicating a patch number corresponding to the instrument. Such patch numbers are specified by the GM (General MIDI) protocol, which is a standard widely known and accepted in the art. The GM protocol specification is available from the International MIDI Association (Los Angeles, Calif.), and was originally described in an article, "General MIDI (GM) and Roland's GS Standard," by Chris Meyer, in the August, 1991, issue of Electronic Musician, which is incorporated herein by reference.
According to GM, 128 sounds, including standard instruments, voice, and sound effects, are given respective fixed patch numbers, e.g., Acoustic Grand Piano =1; Violin =41; Choir Aahs=53; and Telephone Ring=125. When any one of these patches is selected, that patch will produce qualitatively the same type of sound, from the point of view of human auditory perception, for any one key on the keyboard of the digital musical instrument as for any other key. For example, if the Acoustic Grand Piano patch is selected, then playing middle C and several neighboring notes produces piano-like sounds which are, in general, similar to each other in tonal quality, and which vary essentially only in pitch. (In fact, if the musical sounds produced were substantially different in any respect other than pitch, the effect on a human listener would be jarring and undesirable.)
MIDI allows information governing the performance of 16 independent simulated instruments to be transmitted effectively simultaneously through 16 logical channels defined by the MIDI standard. Of these channels, Channel 10 is uniquely defined as a percussion channel which, in contrast to the patches described hereinabove, has qualitatively distinct sounds defined for each successive key on the keyboard. For example, depressing MIDI notes 40, 41, and 42 yields respectively an Electric Snare, a Low Floor Tom, and a Closed Hi-Hat. MIDI cannot generally be used to set words to music. It is known in the art, however, to program a synthesizer, such as the Yamaha PSR310, such that depressing any key (i.e., choosing any note) within one octave yields a simulated human voice saying "ONE," with the pitch of the word "ONE" varying responsive to the particular key pressed. Pressing keys in the next higher octave yields the same voice saying "TWO," and this pattern is continued to cover the entire keyboard.
Some MIDI patches are known in the art to use a "split-keyboard" feature, whereby notes below a certain threshold MIDI note number (the "split-point" on the keyboard) have a first sound (e.g., organ), and notes above the split-point have a second sound (e.g., flute). The split-keyboard feature thus allows a single keyboard to be used to reproduce two different instruments.